Catalytic cracking system



Patented Oct. 29, 1946 CATALYTIC CRACKING 'SYSTEM Robert C. Gunness, Chicago, Ill., :and Joseph W. Jewell, Summit, N. J., assignorsof one-.half 'to Standard Oil Company, a corporation of lInldiana, and one-half to The M. W. Kellogg vCompany, a corporation of Delaware App'lieationmpril 24, 1941, .serial 16.390304 6'Clams. l Thisv invention relates Lto .a .catalytic cracking system and itpertains more particularly to a large scale 'commercial .method and lmeans for eecting catalytic cracking .in a powdered or fluid-type catalyst system.

In 'the .powdered orv fluid-type catalyst system a powdered catalysteiects the conversion .of gas oil or -heavier "hydrocarbons intogasoline while the .catalystis suspended 'in yhydrocarlzlon vapors. Spent catalyst is separated `from reaction gases and vapors and 'is then .suspended 1in a regeneration vgas whereby carbonaceous deposits `are removed from vthe catalystby controlled oxidation. Regenerated catalyst Ais then separated fromregeneration Agases Vand .returned l.to the cracking Step.

Various proposals have been made-forthedesign of commercial crackingxsystems along the above lines but .the actual `use of 'theprocess has heretofore been limited to 'experimental or laboratory rsystems. An .object of ourinvention'is to provide a v'fluid-type catalytic cracking `system for large commercial units, e..g., .a unit which will convert about 10,000 -barrels .per Vday of charging stock into .large ,yields of .high .quality naphthaswhich .may be 'marketed Aas .premium motor fuels .or which V.may form base stocks for aviation gasoline.

One probleminthe .design of .commercial .-uidtype catalytic cracking .systemsis .thatoff utilizing the heat developedlin '.there'generation step. An object of ourinvention is .to ,provide an improved method ,and meansforsolving thisproblem. Our object 4is Ato kprovide a .unitary-system wherein a minimum amount of .extraneous heat .or energy will .have to be supplied. wherein vthe .excess .heat in reaction ,.produts, .regeneration gases and recycled regenerated catalyst ismostefectivelyutilized for supplying lhefat `to vthe .fractionation system, for preheating .chargin'gstock .for generating-steam. etc. A further .object is ,to provide .a method and means -for obtainingaccurate .temperature control inall ,partsof the system and/.or minimizing .the .expense of heat en clfiangers .and heatingand Vcooling equipment. ,A very serious problem iin the operation of a uid 4catalyst cracking system is thatof storing and handling .the powdered catalyst, maintaining thecatalyst fluent rinall .parts o'f ,thesystem, preventing .undue catalyst attrition,.minimizing cataly'st losses and transferring catalysts from ,low pressure zones lto .hi-gh ,pressure Zones without the .use of .mechanical ,impellers Which are ,characterized by -low eciency and which .become rapidly worn by erosion or abrasion when called 2 upon to handle the Acatalyst powder. An 'object of our invention is toprov'ide a commercial system'w'here'in catalyst vispneumatically transferred from 'low levels to.highlevelsandwherein itflows by gravity'from 'high Vlevels -to low .levels throughout the entiresystem.

A 'further 'object-is to ,prevent the loss croat@- lyst vnot only from reactor and regenerator'gas'es but from Vaeration 'gases V,and,pneumatic conveyor gases .throughout 'all partsof thejsystemand to remove leven. finely .divided dust 'from all gases vented from 'the system. A furth'er object isto provide improved methods and means forhandling and utilizing the "dust which is separated from vented gases. .A vfurther object'isto provide an improved .system of 'upper and lower catalyst hoppers, cyclone separators. etc. with an e ectro static precipitator so that, the entire system will functionr smoothlyand eiiciently Without overloading at any point and `Without undesirable surges 'in xpressure or losses in jheat. A further Objectis toprovide improved methods andjmeans for obtaining a substantially uniform ymixture of .regenerated catalyst frorn various separation systems sothatthfe distribution ,of particle sizesof catalyst entering :the 'reactor is always substantially the same.

A `further ob'jec'tis to provide van improvedgeneral layout for a 'fluid-type catalytic cracking system whereby the reaction, 'regeneration and fractionation .parts vof the system .are all integrated to formY a unit of maximum eiciency, A further 'object is to insure the V operation of this unitary system and all parts thereof under voptimum conditions of 'temperature'pressure catalyst densitygetc.. in order that maximumjga s oine yields may be obtained, a minimum amount of carbon maybe deposited on the catalyst, valuable kgas oil fractions maybe obtained from the heavier-than-gasoline products, and gas production (particularly "the 'production fof methane, ethane'and ethylene) maybe reduced to a minimum. Other objectsof .the invention will be apparent as the detailed description 'thereof proceeds.

.In 'broad outline our inventionfcontemplates a vertical up-fiow reactor vchamber which discharges .into an enlarged settling 'zone at the base Aof which is an upper hopperffor spent catalyst .and .in the top of which arefcentrifuges for removing practically all of the catalyst from gases and vapors before they leavethe vsettling zone. Catalyst is suspended .in vincoming hydrocarbon vapors, `carriedloy .said vapors Iinto the base of the reactor, and maintained at a density about to 25, preferably 15 to 18 pounds per cubic foot within the reactor at a temperature of about 800 to 1000 F., preferably 900 to 950 F. and a pressure of about atmospheric to 50 pounds, preferably 8 to 15 pounds per square inch. The catalyst-to-oil ratio .in the incoming stream may range from about 1:1 to about 8:1 but is preferably about 4:1. The average vapor contact time in the reactor may be about 4 to 40 seconds, preferably about 10 to 20 seconds. The average vapor velocity through the reactor may be about 0.4 to 4, preferably about 1.5 to Zfeet per second.

The regenerator is a much larger up-flow chamber which is likewise superimposed by an enlarged settling zone at the base of which is an upper hopper for regenerated catalyst and in the top of which are centrifugal separators for removing unsettled catalyst frcm reaction gases before they leave the top of the settling zone. Spent catalyst is introduced to the lower part of the regenerator by means of air and the average vertical velocity of air and combustion gases in the regenerator is about 0.4 to 4.0, preferably about,1.5 or 2 feet per second so that the catalyst density in the regenerator is about 10 to 25. preferably 18 to 20 pounds per cubic foot. A large amount of regenerated catalyst from the upper hopper is recycled through a catalyst cooler to the regenerator and is reintroduced thereto at a temperature of about '750 to 900, preferably about 840 F. Spent catalyst may enter at about 850 to 950 F., preferably about 900 F. The average temperature of catalyst entering the regenerator may be about 850 F. The regeneration may be effected at a temperature of about 950 to 1050 F., preferably about 1000 F. and under a pressure of atmospheric to 50 pounds. preferably about 8 to 16 pounds per square inch. The amount of air required for returning recycled catalyst to the regenerator, in-

troducing spent catalyst into the regenerator and supporting combustion in the regenerator may be about 13 to .15% by weight of the spent catalyst which is charged to the regenerator but will depend of course on the amount of carbonaceous material that must be burned from the catalyst.

Catalyst is maintained in fluent form in all hoppers, standpipes, etc., by means of an inert aeration gas which is usually steam. Aeration gas from all parts of the fresh and regenerated catalyst system is passed through a Cottrell precipitator for the removal of catalyst dust so that catalyst losses are reduced to a minimum. Fresh catalyst may be transferred to an upper hopper and mixed with Cottrell fines before being admixed with regenerated catalyst and charged to the system.

The finer catalyst particles separated by the Cottrell precipitator and by cyclone separators is either agglomerated. reconditioned, or thoroughly mixed with coarser catalyst particles so that ra uniform catalyst mixture is introduced intothe reactor.

The last traces of catalyst may be separated from reaction products in a combination fractionatine.r and scrubbing tower and returned with a small amount of the heavy oil fraction to the reaction zone.

The gas oil feed passes through various heat exchangers to a surge drum or furnace charge 4 drum and another part may supply heat in the fractionation and steam generation system. We may, however, eliminate the surge drum and generate steam directly in regeneration gas or recycle catalyst exchangers.

'Ifhe product fractionation system may thus receive heat from the regeneration system and it may likewise recover traces of catalyst from product gases so that such catalyst may be returned to the reactor. Reaction products are preferably introduced at the base of a combination fractionating tower and scrubber which may be operated at a pressure of about 5 pounds gauge. We may separately remove one or more gas oil fractions as side streams from this tower and a slurry of recovered catalyst in heavy oil as a bottom fraction. We may utilize the heat from the bottom fraction for preheating charging stock and then for the preheating of water from which steam is to be generated. Also, we may utilize the heat from this bottom fraction or from a clean heavy gas oil withdrawn from a point adjacent the tower for reboiling or stripping one or more of the gas oil side streams. The cooled bottoms or heavy gas oil fractions may then be returned to the top of the scrubbing section of the tower for maintaining the desired temperature at this point in the fractionation system.

The gasoline and gases which are taken overhead from the combination fractionating tower and scrubber may be cooled and compressed to a pressure of about 135 to 150 pounds per square inch. After the removal of water the compressed gases and liquids may be charged to a fractionation system forming a part of the unit or may be charged to other fractionation systems which may form a part of the renery in which'the unit is located.

The invention will be more clearly understood from the following detailed description read in conjunction with the accompanying drawing which forms a part of the specification and which constitutes a schematic ow diagram of our improved system.

The invention will be most clearly understood from the detailed description of a preferred embodiment but it should be understood that the invention is not limited to the 'specific charging stocks. operating conditions, and features herein described. The charging stock may be any gas oil or heavier hydrocarbon distillate which is obtained from natural crude petroleum or from hydrocarbon synthesis or from hydrocarbon conversion processes. The operating conditions will necessarily depend upon the activity and physical properties of the specific catalyst and the extent of conversion which is desired. Many modifications and alternatives of the details herein set forth will be apparent from this detailed description to those skilled in the art.

The catalyst is preferably of the silica-alumina or silica-magnesia type and may be prepared by the acid treating of natural clay such as bentonite. exemplied by the commercial Vactivated clay Super-Filtrol, or by synthetlcally prepari ing a powdered silica-alumina or silica-magnesia drum. If the surge drum is employed gas oil may be cycled therefrom through heat exchangers for absorbing heat from hot regeneration gases and regenerated catalyst. A part of this heatedl gas oil maygo to the furnace charge mixture. An excellent catalyst may be prepared byball-milling silica hydrogel with alumina or magnesia using about 2 to 30%, for example about 15% of alumina or magnesia. The ball-milled dough may be dried at a temperature of aboutV 240 F. and then activated by heating toV a temperature of about 900 to 1000o F. l

Another method Vof preparing a highly active y cracking catalyst is toformf a gel from dilute :antan The silica alumina catalyst may be :rendered more stable at high temperatures bythe Aaddition thereto of zirconia lin either smaller or :larger amounts than alumina.

The lball-milled silica m'agnesi'a catalyst vmay Ibe 'improved -by 1pretreating the magnesia with 'a thorium nitrate solution'sotha't the iinished catalyst may, 'for instance, have fthe following composition:

Per cent Silica 66 `Magnesia v c-. 27 .'Ih'ori'a 7 -No invention is claimed in the composition of yCata'lys't'per lse and no further description of the catalyst is therefore necessary.

The `catalyst in this speci'c example is in pow,- deredformwith a 'particle size of about 10 to 100 microns, i. e., with about 50% of the vcatalyst `passing about a 400 meshscreen. The invention is applicable, however, to other'catalyst sizes provided only that the catalyst beof vsuch sizes and density that it may Abe aerat'ed and handled as a uid in 'the manner hereindescribed.

The feed vstock from source -ID may 'be a Mid- Continent gas oil-or van'iixtureof such'gas oil with the gasoil seperated 'from catalytic vor thermal conversion products and in the example herein described the charge may consist Yof 7500 barrels periday of `virgin ygas oi-l and 2500 barrels per day of -gas oil from refinery conversion systems. This charging stock 'may Yhave -a gravity Yof 'about 30 to 35, Vfor example, 31.1 A. P. I. so that the'charging rate may 'be Vabout 126.800 pounds per hour. The stock mayenter heat exchanger II -a-t about room temperature and leaves this Aexcl'lalflger at about 200 F. It may be 1further heated in -eX- changer! 2 to about 290 Rand thenf'by exchanger t3 to about 450 F. -at which temperature 'it may be introduced through line I4 -to gas roil surge drum yI5 which `may -be at -a pressure of 'about 25 pounds per square inch. This drum rr-nayvbefabout 8 to l0 `feet in diameter by v20 feet long.

A part `of the gas oil -which is pumped `from drum i5 by pump I6 through line I'I may be passed vby line I8 around the tubes of catalyst cooler l 9 and returned by line 20 to line -2I Another ypart of the gas oil pumped by pump I6 l through line 'I I may pass through Iline 22. `through iiue gas cooler 23 and thence by pipe -24 -to line 2l. IThe stream from line `ZI is split, a part of it passing by line 25 to furnace charge drum -26 and apart passing through line 21 to various heaters in the fractionation system. After it has Asupplied .heat in the .fractionation system this gas oilis returned :through line 28 to steam generator 29 and thence back through line 30 to storage drum I 5. The temperature of the gas-oil leaving heat exchangers I9 vand v23 is vabout l600 the temperature of the Vgas .oil returning from the Afraction-ation system through line 28 is about 528 and it is admixed with suioient amount of-hotgas oil vfrom line 25 and line v3l so that the gas loil entering the steam generator iis "about 550 F. AThe gas yoil leaving the :steam generator is about '450 F. While a single steam generator is shown in the drawing it should be' understood that a plurality of such generato-rs maybe em- 6 ployed. A`i'l.1so,`it should be 'understood that the temperatures of the gas oil at various points fin the system may vvary and may be different than thosestated in 'th-is rspecic example.

Charging stock from drum 26 viis introduced by pump 132 and line '33 into -coils 34a of lpipe still '35. This pipes'till may lbe designed with three downwardly fired radiant sections lva lower confvectionisection. The charging stock r`from lline 33" may be iirst passed 'through tubes 34a in the lconvection section and then ythrough tubes 53412 in the kfirst downwardly red radiant section. 'Steam from generator 29 is passed by line 3l`-to coils in this radiant section l'and We Amay introduce an -amoun't of steamequvalent to about 5% by weight -o"f the stock charged. The oil may 'enter ycoils y3419 at about '775 F. and about 75 pounds per'squarein-h and ma'yleave thesecoils at aftemperature of 1z'ftb'ou't 840 Ffan'd a pressure of faboutSO pounds per'square Linch. In'coils *31H7 the :charging stock is completely vaporized, 'the introduced Vs'te'arr'i assuring ycomplete vaporiza'tion.

After complete vaporization in series iow through vcoils'b the charge is superheated while passing lin parallel rfiow'through coils y34o inthe second downwardly heated radiant sectionof the furnace. The pressure drop through coils 33117115 relatively low and superheated vapors may leave these coils at atemperature ofabout'9001'to 1000 F., 'Tio-r `example yabout ^915 F., at a pressure of about 1-8 to -2'0 pounds Aper square inch gage.

"-I'h'e third downwardly 'heated radiant section oi the furnace is employed for superheating steam toa temperature of about 900 F. lor more. The Vsteam may Vbe introduced into the superheating vcoils `through lline 36a, passed through superheating fcoils 3l 'and then distributed to various Lparts of the systemfthrough the'line designated process steam. To avoid unduly complicatin'glthe drawing these process steam distributing lines will be omitted and we will merely indicate ther-points throughout thesystem at which 'process steam is introduced. A part of this su- 'per 'he'atedsteam may be passedthrough line 37a for supplying -loieat or energy in the system or elsewhere and 4another part may be passed through line -Slb'for ad-mixture with steam from generator 29 'and line 36h. A part of the vsteam from l'generator i219 may thus be superhe'ated to various levels 'for any desired use and another part-Cof vthis steam may be passed by line 36e for supplying heat or generatin'gpower in this or any other system. y

.It "should be stated that the charging stock to coils '35a may include about 500 :barrels per day of about 20 LA. P. I. yproduct bottoms containing about 1100 fto 1200 or more pounds per hour of powdered catalyst, this slurry being introduced through 'lin'e 38.

-In addition to vthe 4steam introduced through line 136, steam maybe introduced into the transfer line 39 through line 40 in amount-s of about 41or5% y:by weighto'ffcharging stock. The transfer Pline vapors then pass through line l4I wherein they pick up `powdered catalyst Vfrom -standpipe 4-2. This standpipe may be about 25 or 26 inches inside dia-meter byla'bout '66 'or 67 ffeet high. The pressure above slide valve or star `feeder :43 'mal7 be :'about V19 jor 20 pounds per square inch and the pressure in linen-4l Iat -this point y'maybe'about 141/2 or ylpounds per square rinch. The amount oi catalyst fso introduced `fi`nto 'the hydrocarbon vapors 'is preferably such as t'o ygive a catalystto-oil Weight ratio yof about 4:1 to y5:1 for example about 630,000 to 635,000 pounds per hour olf catalyst may be picked up by the vapor stream at this point. The temperature of this catalyst may be about 950 to 1050 F. and the oil temperature be controlled so that the suspended catalyst-oilmixture may have a temperature of about 950 to 1000 F. This mixture may be introduced into the reactor at a pressure of about 13 pounds per square inch.

The density of the catalyst in entering vapor stream may only be about 1 pound per cubic foot but the catalyst tends to settle into a dense turbulent suspended catalyst phase in the reactor the density of which phase may be about 15 to 18 pounds per cubic foot. Due to the turbulence, i. e., the internal recycling occurring in this dense catalyst phase a substantially uniform temperature prevails throughout the reactor which temperature may be about 900 to 950 F. The reactor may be a cylindrical vessel about 12 or 13 feet inside diameter and about 25 feet high with cone tops and bottoms as illustrated in the drawing. The average vertical vapor velocity in the reactor may be about 1 to 3 feet per second, preferably about 11/2 to 2 feet and the average vapor contact time may range from about to 40 seconds or more, usually about 10 to 16 seconds.

` superimposed above the reactor we provide an enlarged settling chamber 45 which may be about or 16 feet inside diameter by about 35 to 50 feet high. The settling chamber is provided with a cone-shaped bottom which co-acts with the top sides and discharge pipe 46 of the reactor to form an upper hopper for settled and separated catalyst. Pipe 46 may be about 5 or 6 feet in diameter and above this pipe we may provide a baffle 41 for distributing reaction gases and vapors together with suspended catalyst throughout the cross-sectional area of the catalyst separator, thus preventing any chimneying eiect. The density of catalyst in pipe 46 may be only about .6 pound per cubic foot. The vertical upward velocity of gases and vapors in separator 45 may be about ll/z to 2 feet per second. About 1000 to 2000 pounds per hour of process steam is introduced through line 48 and distributor 49 for maintaining settled catalyst in aerated condition and for stripping products therefrom. The low velocity of these aeration or stripping gases, however, permits the catalyst to settle in the upper hopper space and to assume a density of about pounds per cubic foot.

In order to remove as much catalyst as possible from reaction gases before they leave this separation zone we prefer to employ a series of cyclone separators 50, 5I and 52 in chamber 45 each of the separators being provided with dip legs 50d, 5Ia, and 52a extending well below the level of the settled catalyst in the upper hopper. With a pressure in the upper hopper of about 9 pounds per square inch we may have a pressure in primary cyclone 50 of about 81/2 pounds, in secondary cyclone 5| of about 8 pounds, and in tertiary cyclone 52 of about 'l1/2 pounds. The difference between the pressure in chamber 45 and in these cyclones is balanced by the head of settled catalyst in the respective dip legs.

By employing four cyclones in each stage we may remove about 45,000 pounds per hour of catalyst from the iirst stage, about 4,000 pounds per hour from the second and about 1,000 pounds per hour from the third so that the nal gases leaving the separation zone through line 53 will contain only about 800 to 1,200 pounds of unrecovered catalvst per hour.

The `products are introduced at the base of a combination fractionating tower and scrubber 54 which is preferably operated at about ve pounds gauge pressure with a bottom temperature of about 590 F. and a top temperature of about 240 F. A line 55 may be provided for by-passing the charge around the reactor if for any reason the reactor is shut down. The vertical velocities in the reactor may be controlled to a certain extent by varying the amount of steam which is introduced into the charging stock vapors or by by-passing sonne of the charging stock vapors directly to the fractionating tower or by varying the quantity of charge. If the pressure at the base of standpipe 42 falls below safe limits the charging stock is automatically diverted through line 55 bymeans of a pressure controlled valve so that there canV be no possibility of charging stock vapors flowing upwardly in the standpipe and entering the space above the regenerator.

In the base of tower 54 residual catalyst particles are scrubbed out of the reaction products so that they may be returned by line 38 to pipe still coils as hereinabove described. For each volume of bottoms which are so withdrawn we prefer to recycle about 25 or 30 volumes through heat exchanger I3 and one or more coolers 56 back to the scrubbing section of the tower in order to maintain a tower temperature at the top of the scrubbing section of about 580 F. One of the coolers 56 or other heat exchangers in the fractionation system may be employed for preheating the water which is charged to steam generator 29. An emergency draw-off line 51 is provided but is generally not used.

A heavy gas oil fraction may be withdrawn from the tower through line 53 and passed through heat exchanger I2 and cooler 59. Aboutl 2,400 to 2,500 barrels per day of this 25.6 A. P. I. gas oil may be withdrawn from the system through line 60 and another part reintroduced to the tower through line 6I for maintaining the desired temperature gradient. This stream provides the gland oil for various pumps in the system, such oil being introduced to pump glands through line Gla and returned through line lb.

Line G2 is provided for venting any excess gas from surge drum I5 or furnace charge drum 26 to an intermediate point in the fractionating tower. Line 62 is connected by line 62a to surge drum I5 and by line B2b to furnace charge drum 26.

Light gas oil is removed from tower 54 through draw-offs 63 and stripped in side stream stripper 64, the overhead being returned through line 65 to tower 54. The heat for effecting this side stream stripping may be obtained from hot gas oil which is introduced from line 2'1 through line 55 to heat exchanger 5'! and is returned through line 68 to line 28. Indirect stripping is desired in View of the large amount of steam already present in tower 54. About 2,400 to 2,500 barrels per day of 35 A. P. I. gravity light gas oil may be withdrawn through line 69.

About 45,000 barrels per day of liquid may be withdrawn through line 10, passed through heat exchanger I I and cooler 'II and returned through line 'I2 at a temperature of about 150 F. for refluxing the top of the tower so that the overhead from this tower is at a temperature of about 240 F. Due to the large amount of steam present at this point, substantially all of the 400 F. end point naphtha will thus be taken overhead.

The overhead from tower 54 is passed by line 'I3 through cooler 'I4 to. primary low-pressure separator 15 which operates at about 100 F. and

about .atmospheric` orY lpound gauge pressure. Condensed water is removed from this separator throughline '16. The gases from this separator are compressed by compressor 'i1 and the liquids pressurev separator 80. The high-pressure separator is at a temperature.l of about 100 F. but-at a pressure of about l35vto 150 pounds per square inch. Condensed water may be removed from this stage through line'lia. It should be understood that while We. have only illustrated two stages of separation we may use three or more stages, i. e., we may employ an intermediate stage with thev separator at about 25v pounds pressure and wevmay withdraw additional water from this intermediate separator.

Gases from the high pressure separator may be withdrawn through line 8|a to a separate absorber system or introduced through line 8| into the base of absorber 82. Liquids from the high pressure separator may be pumped through line 83av to' a separate fractionation system or maybe pumped through line 33` and heat exchangers 84 and' 84a to an intermediate point in still 85. rlhe heat for this still may be supplied by gas oil from line 2'! and line 85, which leads to heaters 84a and 81, the cooled gas oil being returned through line' 88 to line 25. The bottoms from the still pass through exchanger 84 andI coolerv 39. A part of` this stream amounting to about 3,300 to 3,400 barrels per day may be withdrawn through line Sil-as a 50.3 A. P. I.. heayy naphtha. Another part of this stream is returned byline 9| through cooler 9|@ to the top of tower S2 for absorbing light hydrocarbons from gases which are withdrawn from the system through line 92 for use as fuel or for any other purpose. Rich oilfrorn the base of the absorber is pumped` through line 93 to the still along with liquid from the. highpressure separator 00.

The top of the absorber 32jis connected by lines 92a and 92h to the top of surge drum I5 and by lines 92a and 92e to the top of charge drum 2E. A substantially'constant pressurev is maintained in these drumsgi. e., a pressure of about 25 pounds per square inch in drum |.5 and about 75 pounds per square inch in drum 26 by gases from absorber 82, valve 92dbeing controlled in accordance Withthe desired maximum pressure in drum |and valve- 92e being controlled in accordance with the desired maximum pressure in drum 25. Valves |520v and 62dy are set to relieve at'slightly higher pressures than thatmaintained by-92c and 92h, and since absorber` 82 normally operates under a pressure olr about 135 pounds per square inch we may maintain any ldesired lower pressure in the gas oil drums bythe use of thesev gas lines and Vpressure controlled valves.

The overhead from still 35 is passed through condenser 94 to .receiver 95.A A part` ofthe condensate is recycled through line 96 for useas re flux in the top of still 851 and another partis passed by'line'91f through exchanger |06.; to an intermediate point of` rectifier or stabilizer 98. The heat for the base of thisv stabilizer may be obtained by passing gas oil from line 21 andline 99 through heat exchanger |00`and returning the cooled gas oil through line` |0| back .to line 28. Overhead'from tower' 98 is lcooled in coolerl |02 and introduced into receiver |03. A part ofv this condensate fromthisv receiverzis recycled through line |041fo`r refluxvin tower 98.1 Thebalance of thisy condensate; lwhich mayJ amountl to about :577V

barrels per day, and which consists essentiallyof 10 C3v or a mixture of C3 and C4 hydrocarbons, is Withdrawn through line |05 to a polymerization plant or other system in order that it may be converted into high quality motor' fuel or otherwise e utilized.- The bottoms from tower is Withdrawn through heat exchanger |06v and cooler |01. This fraction may amount to about 1600 to 1700 barrels per day of 98.5 A. P. I. absorption naphtha. y

To recapitulate; .the following products may be Total yield by volumev (i. e..

104.5% on stool; charged) 10,450

The gases separated from receivers. 95.- and |03 may be returned by 1ines95aand1|03a to thefbase of absorber tower 82. In addition tot-he large volumetricvyield of liquidv and liqueed products We obtain about 1,400 to 11,500 pounds per hour of dry gas from fuel gas line 92 and we obtain a considerable amount of heat fromy the carbon which is depositedv on the catalyst. This` heat recovery from carbonaceous deposits on catalysts will noW be described in further detail.

Spent catalyst is. discharged from the upper hopper in chamber 45 to oneor more standpipes |08 of a suitable height tomaintain the desired pressure which in this case may be about 75 to 80 feet. The pressure above the slide valve at the bottom ofV this standpipe may be about 22 to 23 pounds per square inch and the temperature of the catalyst may be about 900 F. Compressed air from line |09 is introduced under` pressure of about 17 or 18 pounds per square inch .and in amounts of about 16,000 to 18,000 pounds. per hour for picking upl catalyst fromthe base of the standpipeand carrying it through line l0v to the base of regenerator chamber This regenerator is. preferably about 1 8 feet inside dia-meter by about 50 feetvhigh.

As inthe caseV of reactorY 44 there isl an enlarged settling chamber ||2 above the regenerator, thisv settling chambery or separatorbeing about 22 feet inside diameter and about 25-to 40 feet high. The inclined upper Wallsof the regenerator terminate in pipev 3 and the spacefbetween pipe ||3 and the walls ofV chamber |r|2 form an upper hopper. for regenerated catalyst. The catalyst Which settles in this 11101161' hOPDeI isv aerated by steam introduced through lineI I4 into distributor ||5.

It is essential that the temperature in the regenerator be maintained within safe limits (from the standpoint of catalyst activity), for example 950 to 1050 F. or about 1000 F. AV considerable amount of the-heat generated by thevcombustion of carbonaceous deposits must be absorbed in and removed fromthe regenerator if the tem'-` perature is tobe held within desired limits. In-

order to control'wthe temperature in' thev regen v eator we recycle about-three times as much catalyst as is introduced through line llvand; wev

cool this recycledcatalyst before itis returned to the regenerator. More specically we w-ith-v draw catalyst'from the upper hopper. inl chamber I2 to one or more standpipes which may beA about feet in height andabout'Z or` 3 feet'inv diameter. The pressure of the catalyst above the lower valve may be about 24 or 25 pounds per square inch. The catalyst in this standpipe as well as in standpipes 42 and |08 are provided with means for introducing aeration steam so that the catalyst is maintained in fluent condition throughout the entire length of the standpipe.

Compressed air from line II'I is introduced at a pressure of about 19 or 20 pounds per square inch and in amounts of about 71,000 pounds per hour. The compressed air picks up the catalyst from the base of standpipe I|6 and conveys it via line II8, through heat exchanger I9 wherein a considerable amount of the heat contained in this recycled catalyst is picked up by gas oil introduced through line I8 and withdrawn through line 20. Heat may be absorbed from the recycled catalyst, by other fluids than gas oil, and if desired steam may be generateddirectly in this exchanger. The temperature of the suspended recycled catalyst at the base of exchanger I3 may be about 950 to 960? F. and the temperature of the suspended catalyst at the top ofl this heat exchanger may be about 940 F. or lower.

When this recycled catalyst is admixed with spent catalyst in the base of regenerator III the average inlet temperature to the regenerator may be about 850 F. but throughout the body of the regenerator a substantially constant temperature of about 1000C F. will prevail. With the amounts of air, regenerator size, and temperatures as above set forth, the vertical velocity of up-ilowing gases in the regenerator should' be about l to 3, or more precisely, about 1% to 2 feet per second. The pressure at the base of the regenerator may be about 16 pounds per square inch and the gases may enter the base of the regenerator at the rate of about/00 cubic feet per second. The pressure at the top of the regenerator maybe about 9 pounds per square inch and the gases may leave the top of the regenerator at the rate of about 650 cubic feet per second. The average density of the catalyst in the regenerator maybe about 18 to 20 pounds per cubic foot.

Baille II-9y distributes the regeneration gases and suspended catalyst uniformly throughout the enlarged separating zone in chamber I2 and the bulk of the catalyst settles out of the gases in this zone. v Y

To obtain more complete catalyst removal we prefer to mount a plurality of cyclone separators in the upper part of the separator. Primary cyclones- |20 may pick up gases through inlet pipe |2I in which gases the catalyst content may be about 375 to 400 grains per cubic foot. The gases discharged from these primary cyclones to secondary cyclones |22 through line |23 may contain only about 75 grains of catalyst per cubic foot. The gases which leave the secondary cyclones through line |24 and enter tertiary cyclones |25 may have a catalyst content of only about 36 grains per cubic foot. The gas discharged from the tertiary cyclones through lines |26 and. |21 may have only about 20 grains of catalyst per cubic foot or less. It should be understood that any-number of cyclones may be employed` in the primary, secondary and tertiary stages and that any number of stages may be used without departing from the invention.

Each cyclone has its dip leg |20a, |22a and |25a which extends lwell below the level ofthe settled catalyst in the upper hopper and the different heads of catalyst in these dip legs compensate for the Vdifference between the pressure in chamber ||2 and the pressures in the respective cyclone separators. The pressure in cham- CII ber |I2 may be about 8 pounds per square inch, there may be a half pound pressure drop through each cyclone separator and about 5 or 6 pounds pressure drop between the top of the separator zone and the discharge end of heat exchanger 23 so that the gases leave this heat exchanger through line |28 at a pressure of about 1 or 2 pounds per square inch gauge.

Instead of single heat exchanger or flue gas cooler 23 we may employ a plurality of such heat exchangers in parallel or in series. The gases may pass downwardly through the exchanger instead of upwardly, as shown. The ilue gases are cooled from about 1000 F. to about 675 F. in these exchangers and the gas oil is heated from about 450 to about 600 F. as hereinabove described. Other heat exchange uid than gas oil may, of course, be used and the cooling may be to different temperatures than those given in this example.

The gases from line |23 are introduced at the base of Cottrell precipitator |29 at a pressure of about 1/2 pound per square inch gauge. They are withdrawn therefrom through line |2911 to a suitable stack at about atmospheric pressure.

The upper hopper in chamber II2 only holds enough catalyst for about a 5 to 20 minute operation of the reactor and in order to insure a substantially constant catalyst level in this upper hopper we provide a large used catalyst hopper |30 which may be about 20 feet in diameter and about 45 or 50 feet high. If the level in the upper hopper rises above desired limits regenerated catalyst is Withdrawn through standpipe H6 and line |3| to the used catalyst hopper |30. If the catalyst level in the upper hopper gets too low, used catalyst from this hopper is introduced into the upper hopper through line |32 by means of process steam introduced through line I 33. Thus a substantially constant level of catalyst in the upper hopper is always maintained.

Fresh catalyst is introduced into the system from hopper |34. Instead of introducing this i fresh catalyst directly with regenerated catalyst we prefer to first admix it With catalyst fines discharged from the Cottrell precipitator. catalyst is picked up by air from line |35 and introduced by line I 36 to an upper hopper |31 the air being separated from the catalyst in this upper hopper and introduced through lines |38 and |39 into the base of the Cottrell precipitator. The fines from the base of the Cottrell precipitator are discharged into hopper |40 (which may f be in the lower part of theprecipitator itself) and are there admixed with fresh catalyst introduced from hopper |31 through line I4'I. The fresh catalyst thus introduced is to replace catalyst losses from the system and it may amount to only about to 170 p'ounds per hour. This amount of catalyst does not supply the desired amount of coarse material for the fines and we, therefore, introduce about fty times as much regenerated catalyst from line |42 as-is ,introduced through line IlII, This mixture of fresh and regenerated catalyst with the Cottrell fines not only serves to add sufficient coarse material to obtain a desired catalyst consistency but it likewise raises the temperature of the fresh catalyst and Cottrell fines so that the resulting mixture will be about 820 F.'

If the Cottrell precipitator were mounted at a sufficiently high elevation the pressure at the base of standpipe |43 might be sufficiently great to permit direct introduction of the catalyst'fmes Fresh mixture back to' upper hopper in chamber H2. With the lower mounting the pressure at the baseiQff standpipe M3 may be only about 6 or 7 pounds per` square inch; We, therefore, pick up: this catalyst mixture at the base of standpipe |;4;3 with process steam introduced through line I'Mfand--convey it through line |45 to any upper hoppen |46, the separated steam being discharged through line |41 into line |28 and Cottrellprecipitator |29.,` Standpipe |48 depending from-hopper |46 may beV of suiiicient length, i. e., about 50 to 60 feet, to give a pressure at itsbase of about 12er 13,pounds per square inch. Catalystjy may be picked upy from the basel of this s tandpipe byrstearnl introduced through line |49 andconveyed thereby through line |50 into separation chamber H2. y

vvInstead of admixingthe Cottrell fines with coarser catalyst andrreturning it to the system we may withdraw the catalyst rines and rework them into additional catalyst materialof larger particle size.l Thecatalystines may be incorporated into additional silica gel or mixed gels orQ` it 'may be pelleted or agglomerated in any known manner and thereafter crushed, if necessary, to obtain the desired particle size. The particle size of catalyst chargedy to the system may vary through a considerable range andwhile inIthi's'eXample weA employ catalyst of about 300 to 400 imesh, or finer, it should be understood tha-t, we may. entirely remove the finest catalyst powder and'operate with a particle size of 'about 100 todo() mesh or even of about 50 to 200 mesh. Thevapor. velocities in the reactor willyof course, be higher when coarser catalyst` is employed but shouldl in. al1 cases be adjusted to give the desiredde'nse phase conditions.

The catalyst inthe used catalyst hopper and thefresh catalyst hopper must be maintained in aerated condition.y Process steam from. line |5| is employed for.` the aeration gas inthe used catalyst hopper. but air from line |52 may be used foraerating the fresh catalyst hopper. Aerationfg'ases from the top of these hoppers may be withdrawn through lines |53, |54, |55 and |39 tothe baseof Cottrell precipitator |29. The catalyst. in all ofthe standpipesis preferably vaerated with. processvsteam and as hereinabove described all, of this. raerating "gas on the fresh and regenerated catalyst eventually passes through Cottrellprecipitator. |29 before it is discharged from the system.v s

Again it should be pointed out that our inventionisnot limited to the operating detailshereinabove,4 described. It has already been suggested that instead of using gas oil for absorbing ,heat` in exchangersv I9 and 23 we may utilize other heat exchange duid. Infact, the surge drum l5V and the recyclelines associated therewith-.f may be entirely eliminated and We may simply close the valve in line 'I and introduce water through line Ila, preferably water which has been previously treated or preheated. This Water may be converted into steam at a pressure of about 135 to 150 pounds per square inch in exchangers I9 and 23 and the steam so generated may be introduced through line 2|a to line 36 (the subsequent Valve in line 2| being closed). A part of this steam may be introduced in coils dium inexchangers |49` andf23 the gas oil charge may beintroduceddirectly` from line I4 through line |4a to line 25 and thence. to thel furnace charge drum.

Also we have already indicated that' a downwardregeneration gas flow may beemployed in exchanger 23-,and that hopper lllimay be eliminated. vThus they regeneration gases from line may Lbe introduced thro-ugh line |21a into thetopvof exchanger 2'3r and the cooledgases from this exchanger may be conductedY directly by line |28a to the base of Cottrell precipitator |29. By employing a sufciently tall standpipe I431or by using a Fuller-Kenyon pump (a screw pump for forcing powdered solids into a zone of higher pressure) at the base of this standpipe, we may return the Cottrell lignes mixture through line |a and` |50- back to chamber H2 Without the necessity of employing hopper |46. Other modications and alternative procedures. will be apparent from the above description to those skilledin the art.

From the above description it will be seen that wehave accomplished the objects of. our invention andl have provided a unique and remarkably effective commercial system. The heat of regeneration is utilized in the fractionation part of the system for obtaining product separation, it is utilized for supplying heat to the charging stock, and it is utilized for the generation of processsteam which is employed throughout the system as a catalyst conveying andaerating medium. The catalyst storage andhandlingrmeans provides a remarkably effective fiexibility of con.- trol. Catalyst losses are reduced to a minimum.

We claim:

1-. in. apparatus. of the class described, a gas oilsurge drum, a steam generator, a pipestill, a catalyst regeneration system including a heat exchanger, a catalyst conversion system, a product fractionation system including a heat exchanger, meansfor-passing gas oil from said surge drum throughthe heat exchanger included in said regeneration system whereby the gas olisheated r by the heat produced in the regeneration system,

means for passing a part of saidheated gas oil through saidy pipe still, thence through said con- Vversionsystemand thence to said fractionation system, means for passing parts of said heated gas. oilthrough the heat exchanger inv said fractionation system and through said steam generator and thence back to said gas oil surge drum, means for introducing spent catalyst from the conversion'system to the regeneration system and means for introducing regenerated catalyst from theregeneration system to the conversion system.

2, The. apparatus .-dened by claim 1 which includesvmeans for superheating the steam generated in said steam generator and means for introducing said superheated steam to both spent and regenerated catalyst for effecting aeration thereof.

3. A duid-type catalytic cracking system which comprises a gas oil surge drum, a regeneration system containing a heat exchanger, a fractionation system containing a heat exchanger, a steam generation systemmeans for passing gas oil from said surge drum to the heat exchanger in the 34h to facilitate vaporization of charging stock. 70 regeneration System, means for passing hot gas Another part may be introduced through line 35a to steam superheating coils 31. Other parts may be withdrawn from the system through lines 36h and 36e as hereinabove described. When Water is used instead of gas oil as a heat exchange me- 7 5 and means for passing gas oil from said fractionoil from the regeneration system heat exchanger to the fractionation system heat exchanger, means for passing gas oil from said regeneration system heat exchanger to said steam generator,

15 ation system heat exchanger and steam generator respectively back to said gas oil surge drum.

4. A catalytic cracking system which comprises a gas oil furnace charge drum, a pipe still furnace containing gas oil heater coils and steam superheater coils, a reactor, a spent catalyst separator above the reactor, a regenerator, a regenerated catalyst separator above the regenerator, a regenerated catalyst cooler below'the regenerator, a regeneration gas heat exchanger, a product fractionation system including a plurality of heat exchangers, means for introducing a gas oil charging stock through some of said lasty named heat exchangers to said gas oil furnace charge drum and thence through said oil heater coils to said reactor, means for passing catalyst from the regenerated catalyst separator to said reactor along with the heated gas oil vapors from the pipe still coils, means for separating catalyst from reaction vapors in said spent catalyst separator, :means for passing reaction products from said ,spent catalyst separator to said fractionation system, means for passing spent catalyst from :said spent catalyst separator to said regenerator, means for recycling catalyst from said regenerator separator through said catalyst cooler and back to said regenerator, means for utilizing the heat abstracted from the catalyst in the catalyst cooler and from the gasesin the regeneration gas exchanger for the generation of steam, means for passing a part of the generated steam through :said steam superheating coils and means for introducing said superheated steam at a plurality of points in the system for maintaining catalyst in aerated form.

5. rI'he method of effecting catalytic cracking which comprises maintaining a column of silica- :alumina cracking catalyst in aerated condition at fa" temperature of about 1G00Q F., said catalyst having a partielle size below about 100 microns, suspending catalyst from the base of said column in a stream of hydrocarbon charging stock which is higher boiling than gasoline, employing a catalyst-to-oil weight ratio in the general vicinity of 5:1, introducing the catalyst suspended in the charging stock stream at a low point in a conversion Zone, maintaining a pressure in the conversion zone within the approximate range of atmospheric to 50 pounds per square inch, maintaining a temperature in said conversion Zone in the general vicinity of 800 to l000 F., passing hydrocarbon vapors upwardly throughA said conversion zone at a velocity in the general vicinity of 1 to 3 feet per second whereby a dense turbulent suspended catalyst phase is maintained the density of which is within the approximate range of about 10 to 25 pounds per cubic foot, maintaining a sufficient amount of said dense phase catalyst material in said zone to obtain a vapor contact time'within the approximate range of 5 to 40 seconds, settling catalyst solids from upowhv ing vapors in a settling space above said dense catalyst phase, centrifugally separating residual catalyst material from vapors before they are discharged from the conversion Zone, passing vapors from which catalyst has been centrifugally separated into a scrubbing zone, recycling liquid from the base of said scrubbing zone through a cooling zone and back to the scrubbing Zone at a point above the point at which vapors are introduced thereto whereby residual catalyst material is scrubbed out of vapors in said scrubbing zone, returning catalyst scrubbed from said vapors to said conversion zone with charging stock introduced thereto, condensing and removing heavier-than-gasoline components in an initial fractionation Zone immediately above and communicating with said scrubbing zone, removing substantially all gasoline boiling range hydrocarbons overhead from said fractionation zone through a cooling zone to a separating zone prior to subsequent fractionation whereby the scrubbing and initial fractionation are effected at a pressure below conversion pressure and said pressure is supplied by the pressure on stock charged to the conversion zone.

6. A catalytic cracking system which comprises a pipe still furnace containing gas oil heater coils and steam superheater coils, a reactor, spent catalyst separation means, a spent catalyst standpipe, a regenerator, a regenerated catalyst separation means, a'regenerated catalyst standpipe, a regenerated catalyst cooler below the regenerator, a regeneration gas heat exchanger, a product fractionation system including a plurality of heat exchangers, means for introducing a gas oil charging stock through at least some of said last-named heat exchangers and thence through said voil heater coils to said reactor, means for passing separated regenerated catalyst from the regenerated catalyst standpipe to said reactor along with the heated gas oil vapors from the pipe still coils, means for passing separated spent catalyst from the spent catalyst standpipe along with air to said regenerator, means for passing reaction products from the spent catalyst separation means to said fractionation system, means for recycling separated regenerated catalyst through said catalyst cooler and back to said regenerator, means for utilizing the heat abstracted from the catalyst in the catalyst cooler and from the gases in the regeneration gas exchanger for the generation of steam, means for passing a part of the generated steam through said steam superheating coils and means for introducing said superheated steam into at least one of said standpipes for maintaining the catalyst in aerated form therein ROBERT C. GUNNESS.

JOSEPH W. JEWELL. 

